A multidisciplinary approach to comprehensively phenotype obese subjects is required to advance our understanding of the physiological, hormonal and behavioral traits that lead to obesity, weight loss or recidivism. The biological and genetic effectors of behaviors that lead to the obese state are not well characterized and poorly understood in humans. Our research focuses on defining the relationship of physical and neuropsychological traits, metabolism and endocrine function to outcomes in bariatric therapies. The bariatic surgery model is employed to study the effects of weight loss in morbidly obese patients over time. The variation in ultimate weight loss induced by currently popular surgeries, diets and drugs are assessed to determine the associated biobehavioral changes. Studies are conducted at the Mark O. Hatfield Metabolic Unit which allow for state-of-the- art study of energy expenditure, body composition and metabolism. Physical activity and exercise capacity is monitored and food preferences and eating behavior are assessed. Molecular imaging studies using ligands of importance in metabolism, cognition and control of appetite will be integrated with genetic and biobehavioral profiles of each subject. The results of this research will lead to the identification of traits, behaviors and genetic profiles that will predict outcomes of bariatrics therapies and ultimately aid physicians treating this increasing population of patients.